[Jello]

So... very much a work in progress, but here's the general idea.

Several years ago, a mountain burst open, unleashing three beings. Sycophantam, Tenebris and Leoht began wreaking havoc on the nearby cities, creating minions from everyday examples of elements such as fire, darkness, lightning, and more. One of these minions was brought down, and its essence became the first Flare. Researching the Flare, the Rider Belt was made and production began on making weapons to combat the three beings. Volunteers were given armors and took to battle.

However, it was found out that prolonged use of Flares wore the human body out extremely quickly, with a large number of Riders dying in the fallout. Out of options, Androids began being produced as well, to wear the belts and fight for humanity's sake. The human Riders that survived helped to train the Androids, since many of them were too wounded to handle normal jobs.

The story follows Dee, one of said androids, as she learns about the world and people around her, what it means to be a person, and herself.

Main Rider: Kamen Rider Diamond
Name: D-33 "Dee"
Gender: Identifies as female, technically agender
Motif: Gems/Jewelry

Belt: Refiner Driver, a mainly silver belt with a blue light in the center and dark blue plating on each side.
Henshin Device: ID Crystals, which unlock the belt and synchronize with the user's identity to retain user-specific armor. ID Crystals also develop with the user, and more change and grow in power over time. Armors themselves are decided by small objects called Flares, which are made from the essence of defeated monsters and range in theme.
Weapons: Ring Saber, a sword made with a spare of Dee's main Flare, Diamond. It serves as a channeling weapon, allowing her to use much more powerful attacks than she would normally be capable of.

Forms
Geode Breaker: Dee's initial form, made from a prototype ID Crystal and a work in progress Flare. This form's only benefit is its extremely high defense, which rivals the mid-story upgrade for the amount of damage it can take, but at the cost of limited movement and draining power quickly.
Diamond: Her base form made using the Diamond Flare. This form offers lower defense than any other form, but much higher speed and strength than Geode Breaker. Its because of her ability to use this from well that she got her Rider name.
Quartz: Quartz Form is made when the Diamond Flare is swapped out for a Flare obtained from one of the higher up monsters. In Quartz, Dee's defense goes up, but without lowering her speed and damage as extensively as Geode Breaker, making it an alternative to Diamond Form.
Queen of Diamonds: Dee's mid-story upgrade that replaces her base form. After choosing to save a monster who only wishes to live in peace, her ID Crystal changed form, unlocking Queen of Diamonds. This form acts as a combination of her three previous forms, with absurdly high defense, speed and damage.
Engagement Form: Dee's final form, made when she and a former Rider both admitted their feelings for one another. This form uses no Flare, rather employing the former Rider's ID Crystal. In this form, she's capable of utilizing any Flares and even doubling the power she would normally get from them thanks to the dual crystals she uses, allowing for a number of new abilities and combinations.

Just the main Rider for now, but maybe I'll talk about the other two sometime.